The unnamed suspect, who has been charged with the murder of two-month-old Zuri Whitehead, reportedly asked her mother to ask if the baby could sleep over at their house on the night she died.
Baby Zuri's mother, Trina, said the 11-year-old's mother - whom is one of her closest friends - called her and said that they wanted to keep Zuri overnight.
"I never thought my baby would be put in some type of harm"
The girl (who has not been identified due to her young age) and her mother thought Trina deserved a break from caring for the infant.
Trina almost declined the offer because it was so late and she was not prepared, but she relented when they insisted.
She told The Associated Press: "I definitely trusted her. I never thought my baby would be put in some type of harm."
The next morning, the 11-year-old was found holding a battered and bloodied Zuri - who was struggling to breathe or open her eyes.
The tiny tot was quickly rushed to hospital, where tests confirmed that she died of repeated, brutal blows to the head.
Police have said that she suffered massive brain injuries, severe damage to the liver, spleen and kidneys, and extensive internal bleeding, police said.
Heartbroken Trina called Zuri, which means 'beautiful' in Swahili, 'the most perfect baby ever'.
"All she wanted was to be held and loved," she said.
Trina added: "[The girl's mother] called and said she's sorry for what happened.
"She can't believe what's going on."
The eleven-year-old, who is being held in a juvenile detention centre, has entered a 'not guilty' plea.
Police chief Randy Ice added that the girl did not show any remorse adding: "I’m not sure she appreciated the gravity of what she did."